COMP1121 COMP1121 Computers and Computer Computers and Computer

NetworksNetworksRichard HensonRichard Henson

University of WorcesterUniversity of Worcester

April 2008April 2008

Week 10 – The Physical Week 10 – The Physical Layer: Network HardwareLayer: Network Hardware

• By the end of this session you should By the end of this session you should be able to:be able to:Identify and select network hardware Identify and select network hardware

devices for a variety of purposesdevices for a variety of purposesExplain what a hardware driver is how Explain what a hardware driver is how

plug-and-play works plug-and-play works Explain how to install a network card and Explain how to install a network card and

ensure it provides network connectivityensure it provides network connectivity

Transmission MediaTransmission Media

• ““Connection” between computers on a Connection” between computers on a network is essential for sending/receiving network is essential for sending/receiving digital datadigital datadoesn’t need to be overtly physicaldoesn’t need to be overtly physical0’s and 1’s can be transmitted without an 0’s and 1’s can be transmitted without an

apparent physical medium…apparent physical medium…

• Suggestions?Suggestions?

Hardware requirements:Hardware requirements:

• A networking “subsystem” A networking “subsystem” on each computer, on each computer, which links in with the motherboard in some way which links in with the motherboard in some way at one time this always happened via aat one time this always happened via a network card network card

connecting the motherboard via ISA or PCI connectorconnecting the motherboard via ISA or PCI connector nowadays, the networking hardware is often built onto nowadays, the networking hardware is often built onto

the motherboardthe motherboard

• A plug/socket arrangement with the physical A plug/socket arrangement with the physical mediummedium USUALLY… this is a “telephone-type” arrangement to USUALLY… this is a “telephone-type” arrangement to

insulate twisted pair copper cableinsulate twisted pair copper cable• known as RJ45known as RJ45

AT ONE TIME… co-axial cables and connectors like a AT ONE TIME… co-axial cables and connectors like a TV aerial system were usedTV aerial system were used

• known as BNC known as BNC

Network CardNetwork Card software requirementssoftware requirements

• Software interfaces effectively with level 3 Software interfaces effectively with level 3 protocolprotocol nowadays usually IPnowadays usually IP part of operating system networking componentpart of operating system networking component requires allocation of IP addressrequires allocation of IP address

• Level 2 software converts packets into Level 2 software converts packets into “frames” of data“frames” of data

• Level 1 software converts the binary frames Level 1 software converts the binary frames into electricity (high/low voltage) and sends into electricity (high/low voltage) and sends them out onto the physical mediumthem out onto the physical medium

Network CardNetwork Card software requirementssoftware requirements

• Each card gets a unique identifier Each card gets a unique identifier during manufactureduring manufactureknown as the MAC address – where “MAC” known as the MAC address – where “MAC”

(media access control) is part of the data (media access control) is part of the data link layerlink layer

• Provides software for physical Provides software for physical signal/binary number interconversionsignal/binary number interconversionOSI layer 1 signals - converts to layer 2 OSI layer 1 signals - converts to layer 2

framesframesOSI layer 2 frames converted to layer 1 OSI layer 2 frames converted to layer 1

signalssignals

Binding Network Card Binding Network Card Software to an operating Software to an operating system “protocol stack”system “protocol stack”

• Two way process:Two way process: Down: Level 3 IP packets need to be converted to Down: Level 3 IP packets need to be converted to

framesframes Up: Level 2 frames need to be converted to IP-Up: Level 2 frames need to be converted to IP-

compatible packetscompatible packets

• As with other hardware devices…As with other hardware devices… achieved through software called “drivers”achieved through software called “drivers”

• Plug-and-play hardware can tell the operating Plug-and-play hardware can tell the operating system what it is and provide the relevant system what it is and provide the relevant software on network card ROMsoftware on network card ROM otherwise, driver software will be needed…otherwise, driver software will be needed…

Transmission MediaTransmission Media

• From the network card/adaptor port, data can From the network card/adaptor port, data can be physically transmitted in a number of be physically transmitted in a number of ways:ways: via insulated copper cablevia insulated copper cable via optical fibre cablevia optical fibre cable via “wireless” media e.g. radio waves, via “wireless” media e.g. radio waves,

microwaves, infra-red beams, etc.microwaves, infra-red beams, etc.

• Transmission medium type greatly affects the Transmission medium type greatly affects the overall speed and resilience of the network overall speed and resilience of the network and the number of packets that get corruptedand the number of packets that get corrupted

Transmission MediaTransmission Media - Cabling - Cabling

• Two types of cables have historically been Two types of cables have historically been used in LANs:used in LANs: thin Coaxial – up to 200 metres per cable runthin Coaxial – up to 200 metres per cable run thick Coaxial – up to 500 metres per cable runthick Coaxial – up to 500 metres per cable run

• Most cabled networks nowadays use either:Most cabled networks nowadays use either: Unshielded Twisted Pair (UTP) – up to 100 metresUnshielded Twisted Pair (UTP) – up to 100 metres Fibre-Optic – up to 1 km per cable runFibre-Optic – up to 1 km per cable run

Transmission Media – WirelessTransmission Media – Wireless

• ““Wireless” means transmission using electro-Wireless” means transmission using electro-magnetic radiationmagnetic radiation means an electro-magnetic wave vibrating with a means an electro-magnetic wave vibrating with a

specified frequency and moving forwards at the specified frequency and moving forwards at the speed of light…speed of light…

light itself is electromagnetic radiationlight itself is electromagnetic radiation

• We take wireless for granted now, but it was We take wireless for granted now, but it was first used to transmit and receive signals only first used to transmit and receive signals only about 100 years agoabout 100 years ago theoretically shown to be possible by Maxwell, UKtheoretically shown to be possible by Maxwell, UK invention usually attributed to Marconi, Italianinvention usually attributed to Marconi, Italian

Discovery of Discovery of Electro-magnetic RadiationElectro-magnetic Radiation

•Potential existence of radio waves were Potential existence of radio waves were predicted in 1864predicted in 1864 an amazing piece of maths…an amazing piece of maths…

•Started almost 30 years before Marconi with Started almost 30 years before Marconi with Cambridge professor James Clerk MaxwellCambridge professor James Clerk Maxwell successfully predicted most of the physical laws successfully predicted most of the physical laws

about propagation and speed of radio waves about propagation and speed of radio waves • noted their resemblance to light wavesnoted their resemblance to light waves• showed how they could be reflected, absorbed and showed how they could be reflected, absorbed and

focused like the beam from a torchfocused like the beam from a torch• and could change the very nature of the object on and could change the very nature of the object on

which they were focusedwhich they were focused

Putting Theory into Putting Theory into PracticePractice

•Hardly anybody believed Maxwell in 1864!Hardly anybody believed Maxwell in 1864! BUT his theory was quantified by Oliver BUT his theory was quantified by Oliver

Heaviside into two equationsHeaviside into two equations

•Over the next 30 years they became a Over the next 30 years they became a physical realityphysical reality in 1879, Prof. David Hughes walked up Portland in 1879, Prof. David Hughes walked up Portland

Place, London with a device that picked up Place, London with a device that picked up transmitted radio wavestransmitted radio waves

in 1887, German scientist Heinrich Hertz carried in 1887, German scientist Heinrich Hertz carried out a famous set of experiments that provedout a famous set of experiments that proved• that Maxwell had been right all alongthat Maxwell had been right all along• that some materials reflected radio waves back…that some materials reflected radio waves back…

in 1894, the British scientist Oliver Lodge in 1894, the British scientist Oliver Lodge transmitted wireless signals over 150 yardstransmitted wireless signals over 150 yards

First Data Transmission by First Data Transmission by Radio wavesRadio waves

•An Italian in London…An Italian in London… ref: ref:

http://www.connected-earth.com/Galleries/Telecommunicationsage/Awirelessworld/Thehttp://www.connected-earth.com/Galleries/Telecommunicationsage/Awirelessworld/Theoriginsofradio/index.htmoriginsofradio/index.htm

Marconi arrived in 1895, 21 years old, with a new Marconi arrived in 1895, 21 years old, with a new system of 'telegraphy without wires' system of 'telegraphy without wires' • had already approached the Italian government - but it had already approached the Italian government - but it

showed no interest. showed no interest. 1896: 1896:

• called upon the Engineer-in-Chief of the Post Office to called upon the Engineer-in-Chief of the Post Office to demonstrate his systemdemonstrate his system

• allowed him to set up his transmitter on the roof of the allowed him to set up his transmitter on the roof of the Central Telegraph Office, and a receiver on the roof of a Central Telegraph Office, and a receiver on the roof of a building 300 yards away. building 300 yards away.

• On July 27 succeeded in sending morse code signals On July 27 succeeded in sending morse code signals between the two locations - world's first recorded wireless between the two locations - world's first recorded wireless message. By 1901, signals had crossed the Atlantic!message. By 1901, signals had crossed the Atlantic!

What vibrates, in electro-What vibrates, in electro-magnetic waves?magnetic waves?

•Put simply:Put simply: electricity through a coil produces a magnetic electricity through a coil produces a magnetic

effecteffect magnetism through a coil generates electricitymagnetism through a coil generates electricity

• If the electricity is varied, or “pulsed”, the If the electricity is varied, or “pulsed”, the magnetic field will also pulse at the same magnetic field will also pulse at the same raterate magnetism travels even through a vacuummagnetism travels even through a vacuum can be used to carry a signalcan be used to carry a signal

•Maxwell’s brainwave was suggesting that Maxwell’s brainwave was suggesting that this effect could be used to transmit signals this effect could be used to transmit signals without wireswithout wires need a energy source, & transmitter/receiver coilsneed a energy source, & transmitter/receiver coils

Transmission Media – WirelessTransmission Media – Wireless

• Data carried most efficiently nowadays on Data carried most efficiently nowadays on extremely high frequency radio waves:extremely high frequency radio waves:patented as “radar”; now called microwavespatented as “radar”; now called microwavesused in ww2 - bounced off enemy planesused in ww2 - bounced off enemy planes

http://www.fi.edu/weather/radar/video/ /historyrad.movhttp://www.fi.edu/weather/radar/video/ /historyrad.mov

• Less bandwidth & lower reliability than Less bandwidth & lower reliability than optical fibre or cable, but becoming very optical fibre or cable, but becoming very popular… e.g.popular… e.g. Cellular Mobile Phone networksCellular Mobile Phone networks

• Connecting mobile phones to each other & the InternetConnecting mobile phones to each other & the Internet Satellite microwaveSatellite microwave

• Data to/from satellite in geocentric orbit (22300 miles up!)Data to/from satellite in geocentric orbit (22300 miles up!)

Transmission Media - WirelessTransmission Media - Wireless

• Point-point microwavePoint-point microwave data transmitted either across roofs of adjacent data transmitted either across roofs of adjacent

campus buildings, or “line of sight” point-point campus buildings, or “line of sight” point-point across open land (up to 30 miles away)across open land (up to 30 miles away)

• Radio waveRadio wave Either “spread-spectrum” or “narrow-band”Either “spread-spectrum” or “narrow-band” Useful for connectingUseful for connecting mobile laptops to a LANmobile laptops to a LAN

Mechanism of data transferMechanism of data transfer

• Coaxial or twisted pair:Coaxial or twisted pair: data is transmitted by electrical conductiondata is transmitted by electrical conduction cabling system consist of twocabling system consist of two (or groups of two) (or groups of two)

conducting wiresconducting wires

• Fibre opticFibre optic Data transmitted by light internally reflected Data transmitted by light internally reflected

through a thin through a thin fibrefibre-glass tube-glass tube Data can be safely transmitted separately in both Data can be safely transmitted separately in both

directionsdirections

Cabling and CrosstalkCabling and Crosstalk

• Two parallel wires, as Two parallel wires, as used in used in domesticdomestic electricalelectrical cabling cabling, cannot be used for data, cannot be used for data

• Reason -Reason - “crosstalk”: “crosstalk”: electrical interferenceelectrical interference between signals in the two between signals in the two

wireswires signals jumping from one wire to the othersignals jumping from one wire to the other

• The longer the cable, the greater the chance The longer the cable, the greater the chance of crosstalkof crosstalk Therefore there will always be a limit on cable run Therefore there will always be a limit on cable run

between data storage devices between data storage devices

Crosstalk and Crosstalk and Coaxial CablingCoaxial Cabling

• Magnetic fields produced by electricity in the Magnetic fields produced by electricity in the two wires tends to cancel outtwo wires tends to cancel out

• This greatly reducesThis greatly reduces, but does not eliminate, but does not eliminate cross talkcross talk

• There is a There is a recommended maximum length for recommended maximum length for Ethernet cables for this reason:Ethernet cables for this reason: thin Ethernet - 185 thin Ethernet - 185 metresmetres thick Ethernet - 500 metresthick Ethernet - 500 metres

Thin Coaxial CableThin Coaxial Cable

• Also known asAlso known as:: Thin EthernetThin Ethernet Base bandBase band

• CCable consists ofable consists of:: single copper central wire covered with a layer of single copper central wire covered with a layer of

insulationinsulation itself covered by wire braiding (a patchwork made itself covered by wire braiding (a patchwork made

of very thin copper wire)of very thin copper wire) WWhole arrangement wrapped in a (usually black) hole arrangement wrapped in a (usually black)

plastic tubeplastic tube

Thin Coaxial CableThin Coaxial Cable

• AAlso known as IEEE 10base2lso known as IEEE 10base2 IEEEIEEE - Institute of Electrical and Electronic - Institute of Electrical and Electronic

Engineers (more on this erudite body later)Engineers (more on this erudite body later)

• NotNot very flexible because of the nature of its very flexible because of the nature of its constructionconstruction

• AAvailable in a range of different qualitiesvailable in a range of different qualities

• GGenerally used for networks using a bus enerally used for networks using a bus topologytopology

• RRecommended maximum data transmission ecommended maximum data transmission raterate - - 10Mbits/sec10Mbits/sec

Connecting Thin Coaxial CableConnecting Thin Coaxial Cable

• ComputersComputers connected to aconnected to a thin coaxial thin coaxial bus bus network need a network card with a BNC network need a network card with a BNC socketsocket

• Such network cards are becoming very rare…Such network cards are becoming very rare…

• The coaxial The coaxial bus bus connects to the network card connects to the network card through a metal BNC “T connector”through a metal BNC “T connector”

• The The coaxial coaxial cable itself must be “terminated” at cable itself must be “terminated” at each end with a BNC “terminator”each end with a BNC “terminator” that that completes the electrical circuitcompletes the electrical circuit

Thick Coaxial CableThick Coaxial Cable

• Also known as Also known as Thick EthernetThick Ethernet or or broadbandbroadband cablecable very expensive and cumbersome to use…very expensive and cumbersome to use…

• Includes two shielding layers between the Includes two shielding layers between the wires to allow for “harsh” environments (lots of wires to allow for “harsh” environments (lots of electrical “noise” caused by nearby electric electrical “noise” caused by nearby electric motors, etc.)motors, etc.)

• Superior to thin Ethernet is two ways:Superior to thin Ethernet is two ways: Higher data transmission rates (100Mbits/sec recd Higher data transmission rates (100Mbits/sec recd

maximum)maximum) Larger cable lengths (500 metres recd. maximum)Larger cable lengths (500 metres recd. maximum)

Twisted Pair CableTwisted Pair Cable

• The current standard in most LANsThe current standard in most LANs

• Compared to coaxial:Compared to coaxial: ccheaperheaper much more flexiblemuch more flexible easy to useeasy to use doesn’t need BNC T connectors or terminatorsdoesn’t need BNC T connectors or terminators

• Twisted Pair construction tends to cancel out Twisted Pair construction tends to cancel out magnetic fields - greatly reducing cross talk magnetic fields - greatly reducing cross talk (but not as effectively as coaxial)(but not as effectively as coaxial)

Twisted PairTwisted Pair v Thin Coaxialv Thin Coaxial - - Disadvantages Disadvantages

• UUse of se of the the “twisted pairs” - wrapping the “twisted pairs” - wrapping the individual wires around one another - does individual wires around one another - does not reduce cross talk as effectively as coaxial not reduce cross talk as effectively as coaxial cablecable

• More More susceptible to “ harsh” environmentssusceptible to “ harsh” environments (especially rapidly changing magnetic fields)(especially rapidly changing magnetic fields) Extra insulation of twisted pair cable Extra insulation of twisted pair cable

recommended in such circumstancesrecommended in such circumstances Cable therefore becomes more expensiveCable therefore becomes more expensive

Topology - Twisted Pair CableTopology - Twisted Pair Cable  

• Normal use - Star topologyNormal use - Star topology

• ConnectionsConnections could could go directly from network go directly from network cardcard sockets sockets to hub portsto hub ports using RJ45 plastic end connectorsusing RJ45 plastic end connectors similar to RJ11 telephone line connectors (similar to RJ11 telephone line connectors (but not but not

the same!the same!))

• In practice, for flexibility, a combination of In practice, for flexibility, a combination of CAT5 cables, connectors, patch leads/sockets CAT5 cables, connectors, patch leads/sockets used to used to connect network cardsconnect network cards to hubsto hubs

• Most modern network cards are known as Most modern network cards are known as “combo” - this means they have sockets for “combo” - this means they have sockets for both BNC (coaxial) and RJ45 (twisted pair)both BNC (coaxial) and RJ45 (twisted pair)

EIA/TIA Cabling EIA/TIA Cabling StandardsStandards for for Twisted Pair cableTwisted Pair cable

• EIAEIA - - Electronics Industries AssociationElectronics Industries Association

• TIA - Telecommunications Industries AssociationTIA - Telecommunications Industries Association

• EIA/TIA is a EIA/TIA is a Cabling standards Cabling standards bodybody joint venturejoint venture between the EIAbetween the EIA & TIA & TIA

• The EIA/TIA 568 standard covers five types of The EIA/TIA 568 standard covers five types of unshielded twisted pair cable known as (in unshielded twisted pair cable known as (in increasing quality) CAT1 through to CAT5increasing quality) CAT1 through to CAT5

• CAT5 standard has evolved to CAT5fCAT5 standard has evolved to CAT5f

Existing EIA/TIA 568 standardsExisting EIA/TIA 568 standards

• CAT1CAT1 is OK for voice communications, but not is OK for voice communications, but not suitable for digital datasuitable for digital data

• CAT2CAT2 can only support digital data transfer rates of up can only support digital data transfer rates of up to 4 Mbits/secto 4 Mbits/sec

• CAT3CAT3 can only support digital data transfer rates of up can only support digital data transfer rates of up to 10 Mbits/sec (this is the lowest standard for IEEE to 10 Mbits/sec (this is the lowest standard for IEEE 802.3 10BaseT Ethernet networks802.3 10BaseT Ethernet networks - - next week’s next week’s session)session)

• CAT4CAT4 can only support digital data transfer rates of up can only support digital data transfer rates of up to 16 Mbits/secto 16 Mbits/sec

• CAT5CAT5 can officially handle up to 100 Mbits/sec, can officially handle up to 100 Mbits/sec, although it although it isis be beinging used on faster ( used on faster (e.g. e.g. 155Mbit/sec) 155Mbit/sec) FDDI networksFDDI networks

• CAT6 can handle faster rates, theory up to 1 GigabitCAT6 can handle faster rates, theory up to 1 Gigabit

Features of Twisted Pair CableFeatures of Twisted Pair Cable

• MMost popular type currently ost popular type currently known asknown as Category 5 UTP (unshielded twisted pair)Category 5 UTP (unshielded twisted pair) 5e still widely used5e still widely used 5f, 65f, 6 currentcurrent preferred standards preferred standards CAT5e upwards cCAT5e upwards can carry data at an carry data at high high transmission transmission

rates rates ((up to up to 200200 Mbits/sec Mbits/sec)) CAT5f, CAT6: even higher (1 Gigabit/sec)CAT5f, CAT6: even higher (1 Gigabit/sec)

• BBecause of the greater susceptibilityecause of the greater susceptibility of twisted of twisted pair pair to cross talk, the maximum recommended to cross talk, the maximum recommended cable length for CAT5 is 100 metrescable length for CAT5 is 100 metres

Optical Fibre Cable - Optical Fibre Cable - constructionconstruction

• The cable itself consists ofThe cable itself consists of:: a glass or plastic central light conductora glass or plastic central light conductor surrounded by a further layer of glass or plastic surrounded by a further layer of glass or plastic

claddingcladding and a protective outer casingand a protective outer casing

• The cable must be connected directly to:The cable must be connected directly to: light emitter (one end)light emitter (one end) light detector (other end)light detector (other end)

Optical Fibre CableOptical Fibre Cable

• First of all, the electrical signal needs to be First of all, the electrical signal needs to be converted into light pulses. This done by:converted into light pulses. This done by: either an LED (light emitting diode) either an LED (light emitting diode) or a Laser or a Laser

• The light pulses are then directed into the The light pulses are then directed into the central tubecentral tube

• The light is repeatedly totally internally The light is repeatedly totally internally reflected as it passes along the inside of the reflected as it passes along the inside of the tube - as if it were on the inside of a mirrortube - as if it were on the inside of a mirror

Optical Fibre Cable (continued)Optical Fibre Cable (continued)

• Thanks to total internal reflection, a cable can Thanks to total internal reflection, a cable can carry light considerable distances, including carry light considerable distances, including round bends, without significant energy lossround bends, without significant energy loss 1 km cable run quite possible…1 km cable run quite possible… cable must be bent carefully, otherwise internal cable must be bent carefully, otherwise internal

structure could be damaged…structure could be damaged…

• On emerging from the cable, the pulse is On emerging from the cable, the pulse is converted back into an electrical signal by a converted back into an electrical signal by a photodiodephotodiode

• More detail:More detail: http://www.http://www.arcelectarcelect.com/.com/fibercablefibercable..htmhtm

Optical Fibre Cable - Optical Fibre Cable - advantagesadvantages

• Speed of transmission (up to Gbits/sec)Speed of transmission (up to Gbits/sec)

• Ability to support voice and digital data along Ability to support voice and digital data along the same cablethe same cable

• Security (very difficult to tap) and reliability of Security (very difficult to tap) and reliability of transmission (almost immune to electrical transmission (almost immune to electrical interference)interference)

• A pair of optical fibres can simultaneously A pair of optical fibres can simultaneously carry light/data in each direction (full duplex)carry light/data in each direction (full duplex) with no danger of signal attenuationwith no danger of signal attenuation WithWith copper cable copper cabless, signals , signals in adjacent cablesin adjacent cables

ccould interfere with each otherould interfere with each other

Optical Fibre Cable - Optical Fibre Cable - disadvantagesdisadvantages

• EExpensivexpensive

• ExpensiveExpensive to install to install

• Not as flexible to use in tight areas of twisted Not as flexible to use in tight areas of twisted pairpair

• Needs expensive hardware to reliably convert Needs expensive hardware to reliably convert light into electricity and vice versalight into electricity and vice versa

HealtHealth, h, SafetySafety & & Transmission MediaTransmission Media

• Some people object to cable being visibleSome people object to cable being visible apart from aesthetic reasons, also a potential safety apart from aesthetic reasons, also a potential safety

hazardhazard

• DDifferent types of twisted pair cable are ifferent types of twisted pair cable are availableavailable forfor different environments (e.g. under different environments (e.g. under carpets or in the plenum space above a carpets or in the plenum space above a “lowered” ceiling“lowered” ceiling))

• TThis usually increases the likelihood of his usually increases the likelihood of crosstalk, and effectively reduces the crosstalk, and effectively reduces the recommended minimum cable lengthrecommended minimum cable length

• Standards laid down by IBM in the 1980s…Standards laid down by IBM in the 1980s…

IBM Cabling IBM Cabling CategorCategoriesiesCategory Contents Purposes Type 1 Shielded Twisted Pair x2

with casing Data

Type 2 as above, with further 4 pairs added outside the shield for voice

Data & Voice

Type 3 4 twisted pairs unshielded (as above)

Voice

Type 5 2 x 62.5/125 micron Optical Fibre

Data

Type 6 as 1, with foil-braid shield Data (2/3 distance limits of category 1)

Type 8 as 1 - flattened Data (under carpets - 1/2 distance limits of category 1)

Type 9 as 1 - fire-resistant case (e.g. PVC)

Data (in plenum space above ceiling)